Abstract: SichuanTibet Railway is the most challenging railway project worldwide to date due to its great elevation difference, intensive tectonic activities, frequent mountain disasters, fragile ecological environment and severe hypoxia at high altitude. In this paper, the challenges to be encountered during TBM construction for SichuanTibet Railway under various complex conditions, including numerous long and large tunnels, high insitu stresses, and highly active faults etc., are described in details. Innovative design concepts and characteristics of TBMs for construction of SichuanTibet Railway are systematically analyzed in eight aspects such as alpinecold condition, longdistance driving in hard rock and rockburst etc. From these analysis, conclusions are drawn as follows: (1) Advanced geological probing and treatment is a main means of risk control for TBM tunneling during construction of SichuanTibet Railway tunnels. (2) It is particularly necessary to adopt innovative design TBM with "dual shield + rock bolt & shotcrete" or dualsupport TBM for constructing rockburst prone tunnels. (3) For tunnels prone to large deformation, open dualmode TBMs or TBMs with innovative structure design are preferred. It is expected to provide some reference for targeted TBM design and tunnel construction in the later stage.

Key words: SichuanTibet Railway, extralong tunnel, TBM, alpinecold condition; high insitu stress, high ground temperature, adverse geological conditions